Neurostimulation systems are devices that generate electrical pulses and deliver the pulses to nerve tissue to treat a variety of disorders. Spinal cord stimulation (SCS) is the most common type of neurostimulation. In SCS, electrical pulses are delivered to nerve tissue in the spine typically for the purpose of chronic pain control. Applying electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce “paresthesia” (a subjective sensation of numbness or tingling) in the afflicted bodily regions which can effectively mask the transmission of non-acute pain sensations to the brain.
Neurostimulation systems generally include a pulse generator and one or more leads. The pulse generator is typically implemented using a metallic housing that encloses circuitry for generating the electrical pulses, control circuitry, communication circuitry, a rechargeable battery, etc. The pulse generating circuitry is coupled to one or more stimulation leads through electrical connections provided in a “header” of the pulse generator.
Each stimulation lead includes a lead body of insulative material that encloses wire conductors. The distal end of the stimulation lead includes multiple electrodes that are electrically coupled to the wire conductors. The proximal end of the lead body includes multiple terminals, which are also electrically coupled to the wire conductors, that are adapted to receive electrical pulses. The distal end of a respective stimulation lead is implanted at the location adjacent or within the tissue to be electrically stimulated. The proximal end of the stimulation lead is connected to the header to the pulse generator or to an intermediate “extension” lead.
The manufacture of stimulation leads is a relatively complex process. Some manufacturing techniques involve wrapping conductor wires with insulative coatings about a mandrel in a helically manner. An example of a system adapted to perform such winding is shown in U.S. Pat. No. 7,287,366, entitled “Method for producing a multielectrode lead,” which is incorporated herein by reference. The system described in the '366 patent draws a mandrel through wire wrapping structure. As the mandrel is drawn into a spool, conductor wires are let out in controlled manner by a plurality of “payout carriers.” The plurality of payout carriers are rotated as a group about the mandrel. Also, each payout carrier is rotated independently about its own axis to compensate for twist imparted by the group rotation to minimize the amount of residual force left on the wound wires. The final product in the '366 patent is a product with multiple conductor wires wound about the mandrel in helical manner. This product is then cut into separate lengths for fabrication of stimulation leads including attachment of electrodes and terminals.
Also, in known wire wrapping systems, force is applied to the wires as the wires are served onto the mandrel to permanently deform or “preform” the wires to maintain the wires around the mandrel when the winding tension is released. The application of force may be implemented using a “winding die.” In operation, the individual wires pass over one or more radii of a circular or toroidal die where the assembly of the wires and the mandrel pass through a center hole of the die.